1. Field of the Invention:
The present invention relates to a viscous fluid coupling which can be used with a fan for cooling an automotive engine.
2. Description of the Related Art:
A conventional viscous fluid coupling according to Japanese patent application No. 62-013859, filed Jan. 23, 1987, and disclosed in related U.S. Pat. No. 4,880,095, is shown in FIG. 4. There, a bimetal 7 as a temperature-responsive member opens a valve 9 via a rod 8 when the ambient temperature is increased to a high temperature. Then, the viscous fluid flows into a fluid chamber divided by a rotor 1 into first fluid chamber 5a and a second fluid chamber 5b, from a first reservoir 6a. Under this condition, torque is transmitted from an input member 2 to a casing 3 as an output member via the rotor 1, and a fan (not shown) rotates. At this time, the fluid is pumped from a second reservoir 6b into the first and second fluid chambers 5a and 5b through a hole 17 in a rear plate 16, via a pump projection 19. Torque-transmission is controlled by a degree of the opening of the valve 9. Element 4 is a cover mounted to the casing 3.
During operation of this viscous fluid coupling, the fluid in the fluid chambers 5a and 5b is also being returned to the first reservoir 6a due to the following pumping action. That is, a pumping action is generated between a casing 3 and plural angled teeth formed on the rotor 1 (FIG. 3), each of which is oriented toward a rotating direction of the rotor 1, thereby returning the viscous fluid to the first reservoir 6a from the first and the second fluid chambers 5a and 5b during rotation of the rotor.
However, the rotational speed of the output rotational member, i.e., the casing 3, varies relative to the rotational speed of the input member 2 for a given detected air temperature. This is shown in FIG. 5. That is, it has been found that for a given detected air temperature the fan speed Nf can be variable, i.e. scatter, within the shaded area.